Cache Guice Injector with TestNG (best way)

CachedModuleFactory.java

/**
 * @author Andrei Varabyeu
 */
public abstract class CachedModuleFactory<T extends Module> implements IModuleFactory {

    private static final Cache<Class<? extends Module>, Injector> CACHE =
            CacheBuilder.<Class<? extends Module>, Injector>newBuilder().build();

    private final Callable<Injector> INJECTOR_LOADER = new Callable<Injector>() {
        @Override
        public Injector call() throws Exception {
            return Guice.createInjector(createParentModule());
        }
    };


    abstract protected T createParentModule();

    abstract protected Class<T> getParentModuleType();

    abstract protected Module createTestModule(ITestContext context, Class<?> testClass);


    @Override
    final public Module createModule(ITestContext context, Class<?> testClass) {
        Module childModule = createTestModule(context, testClass);
        if (testClass.isAnnotationPresent(UseParentInjector.class)) {
            boolean cached = testClass.getAnnotation(UseParentInjector.class).cached();

            Injector injector = cached ? getCached(getParentModuleType()) : Guice.createInjector(createParentModule());
            context.addInjector(Collections.singletonList(childModule),
                    injector.createChildInjector(childModule));
        }
        return childModule;
    }

    private Injector getCached(final Class<T> moduleType) {
        try {
            return CACHE.get(moduleType, INJECTOR_LOADER);
        } catch (ExecutionException e) {
            throw new UncheckedExecutionException(e.getCause());
        }
    }
}

UseParentInjector.java

/**
 * @author Andrei Varabyeu
 */
@Retention(RUNTIME)
@Target({ElementType.TYPE})
public @interface UseParentInjector {
    boolean cached() default true;
}